E l 4NSMonomeric tetrahedral manganese dialkyl tertiary phosphine complexes of stoicheiometry MnR2( PR'3)2 have been identified in solutions by electron spin resonance spectra and the alkyl complex Mn(CH,CMe,Ph),( PMe3), isolated and structurally characterised by X-ray crystallography. The molecule has a severely distorted tetrahedral geometry with P-Mn-P and C-Mn-C angles of 96.2 and 137.9' respectively, which reflect the relative sizes of the two kinds of ligand. The Mn-C and Mn-P distances are 2.1 49(6) and 2.633(4) A respectively. Use of the chelating phosphine, 1,2bis(dimethy1phosphino)ethane (dmpe), has allowed the isolation of the tetrahedral monomers MnR,(dmpe) (R = CH,SiMe3, CH2CMe3, and CH,Ph). The chelate dialkyl o-xylylene, o-(CH2),C6H4, gives an octahedral complex Mn[o-(CH2),C6H4] (dmpe), whose structure has also been determined by X-ray diffraction. In this molecule, all metal-ligand bond lengths are shorter than the corresponding bonds in Mn(CH2CMe2Ph)2(PMe3)2. This is consistent with a significant reduction in the Mn" radius on adoption of the low-spin state observed. The Mn-C distances are 2.1 1 O(5) and 2.1 04(6) A, while the Mn-P distances of 2.230(3) (trans to P) and 2.298(3) a (trans to C) reflect the different trans-influence abilities of alkyls and phosphines. The X-band e.s.r. spectra of the monomeric complexes have been studied in detail and are discussed in terms of distorted tetrahedral high-spin MnI1 and octahedral low-spin MnI1 species.The interaction of manganese(r1) dialkyls with tertiary phosphines has yielded a number of adducts such as Mn2(CH2-SiMe3)4(PMe3)2, which have been shown to be alkyl-bridged dimers by X-ray Crystallography.' A few monomeric adducts of the dialkyls with oxygen-or nitrogen-donor ligands are also known, examples being Mn(CH2CMe3)2(py)2 ' (py = pyridine) and Mn(CH2Ph)2(dioxane)2,3 but these have not been examined crystallographically. We now describe the synthesis and structural characterisation of some monomeric adducts of manganese(r1) dialkyls with tertiary phosphines. The isolated compounds, some properties and analytical data are given in Table 1.
Results and DiscussionAdducts with Unidentate Phosphines.-In the synthesis of the dimeric adducts, Mn2R4(PR'3)2,1 it was noted that the orange colour of the solutions changed to pale yellow on addition of excess phosphine. Although colourless crystals could be obtained from light petroleum solutions of Mn2-(CH2SiMe3)4(PMe3)2 containing excess PMe3, these readily lost phosphine to re-form the dimer. Electron spin resonance spectra of the pale yellow solutions (see later discussion) indicated that tetrahedral monomers were formed by the cleavage reaction (1). Similar behaviour was observed for R = CHz-CMe, and CH2Ph, and with other phosphines.This monomer-dimer equilibrium was utilised in the preparation of M ~I ~( C H ~P ~) ~( P M ~~) ~ ' when this dimer was found to be insoluble in toluene and diethyl ether, and could not be directly separated from magnesium salts also formed in the 7 Supplementary data availa...